SMA: Large-scale storage systems stabilize grid operation

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South Korea will commission the world’s largest battery-storage system by the end of 2015. In the first stage of expansion, 200 MW of reserve power will be provided to stabilize the utility grid there. SMA Solar Technology AG is the only non-Korean manufacturer to have succeeded in winning a contract for one of the seven portions. In the installation, 24 Sunny Central Storage 1000 battery inverters will integrate lithium-ion batteries into the local utility grid. Altogether, the connected load will amount to 24 megawatts.

South Korea is the front-runner when it comes to such projects, and not without reason. In terms of the grid, the country is an island. There is no connection with the transmission lines in the north. Apart from that, the country is surrounded by the sea. This is particularly important when fluctuating renewable energies are expanded. The country cannot exchange any electrical power with neighbors and therefore relies on providing its entire power reserve itself. This is the new battery-storage systems’ task.

South Korea plans a gigawatt of battery-storage capacity

In the years to come, the South Korean government is planning to invite bids for additional large-scale battery-storage power plants in the multi-megawatt range as the economy and thus electricity demand are expected to grow. In addition, the proportion of renewable energy will increase. The capacity of battery-storage systems to provide reserve power is even expected to be increased to a gigawatt.

Battery-storage power plants are not only of interest to isolated grid regions like South Korea. The use and efficiency of battery-storage power plants are being explored in numerous countries. In Germany, for example, the M5BAT system is being studied in Aachen (http://m5bat.de/). The study is examining areas of application and the efficiency of different battery technologies in providing an operating reserve. This makes it necessary to bring together project partners from different fields of technology. The project likewise has the support of the government with sponsorship from the German Federal Ministry for Economic Affairs and Energy. There are also already many megawatt-class installations in commercial use in Europe, for example in Bedfordshire in England and the Wemag storage system in Schwerin in Germany.

So far, provision of grid management services has been the task of conventional power plants. In addition to providing an operating reserve, these grid management services include other intelligent functions required for energy transmission and distribution to ensure secure grid operation. Generation and consumption are adjusted in a multi-step process; depending on the time slot, operating reserve is drawn from the steam cycles of base load power plants, from pumped storage power plants or from rapidly adjustable peak load power plants. Surplus energy can be balanced out in the longer term by being sold to or purchased from neighboring utility grids.

Reducing must-run units with battery inverters and storage systems

The increasing share of renewable energy in the energy supply and its fluctuating grid feed-in also increases the need for flexibility and thus for balancing energy. Large battery inverters like the SMA Sunny Central Storage in combination with on-grid storage systems can provide the grid management services needed to secure grid operations even without conventional power plants. They can take on the frequency-dependent control of active power feed-in, stabilize the voltage with reactive power supply and help reestablish supply after grid failure. Transmission losses and complicated grid congestion management can therefore be avoided just as costly grid infrastructure investments can.

Battery-storage systems thus make volatile generators more manageable and controllable. Their use can reduce the number of conventional “must-run units,” mostly coal-fired power plants. Grid requirements are met and supply reliability is guaranteed at all times. In addition, storage systems can be used as an uninterruptible power supply on weak utility grids and for power exchange trading in electricity purchased at low-cost in phases of low prices.

If operators of steam power plants ran them at maximum load, but provided operating reserve via a battery-storage system, these power plants would work much more efficiently: The same amount of fuel would generate more electricity and the battery-storage system would practically finance itself from the additional income resulting from the increase in efficiency.

But what the operation of battery-storage systems on the utility grid still lacks in most markets is sufficient economic and regulatory conditions to guarantee long-term investment security for operators. In this aspect, the South Korean example is still an exception. But that will presumably change. The medium-term opportunities for the use of large battery-storage systems for grid support are therefore exceedingly good.

Volker Wachenfeld is Head of the Off-Grid & Storage division at SMA.